1. Technical Field
The invention relates to reinforced resilient pneumatic tires and more particularly to a vehicle tire reinforced by a thin annular composite band which enables the tire to run in an unpressurized condition and to provide greater puncture resistance for the tire. More particularly, the invention relates to a pneumatic tire in which the band element is formed of twisted material strips having fibers which are oriented within the band to extend across the neutral axis of the band and not fall within the axial plane of the neutral axis to provide the band with enhanced ability to resist interlaminar shear stresses and provide enhanced inflated and uninflated banded tire durability and puncture resistance.
2. Background Information
Various tire constructions have been devised over the years which enable a tire to run in an under-inflated or non-inflated condition, such as after receiving a puncture and loss of pressurized air, for extended periods of time and at relatively high speeds. This enables the vehicle operator to safely drive the vehicle to an appropriate location for repair or replacement of the punctured tire. Certain of these safety tires, referred to as xe2x80x9crun flat tiresxe2x80x9d, have been successful for certain applications and certain types of tire constructions. Most of these run flat tires achieve their run flat capability, by the placement of reinforcing layers or members of relatively stiff elastomeric material in the side walls of the tire which enable the tire to support the vehicle weight even with the complete loss of internal air pressure. Examples of such prior art run flat tire constructions which use such sidewall inserts are shown in U.S. Pat. Nos. 3,911,987; 3,949,798; 3,954,131; 4,067,372; 4,202,393; 4,203,481; 4,261,405; 4,265,288; 4,287,924; 4,365,659; 4,917,164; and 4,929,684.
In addition to these prior art run flat tires, various run flat tire constructions have been developed which utilize a thin annular band which extends circumferentially throughout the tire beneath the tread area. Examples of such banded run flat tires are shown in the following patents.
U. S. Pat. No. 4,428,411 describes a method to make a particular band for use in a run flat tire which uses a series of side-by-side elements in the form a helix. The band has hoop compression as against a conventional breaker belt that has no significant compressive strength but is used only to resist tension loads endured by the tire when pressurized.
U.S. Pat. Nos. 4,673,014 and 4,794,966 teach a method to acquire desirable prestressing in a fabricated band made of helical elements. Physically bending the larger diameter helix element around a smaller mandrel and securing it with a resin impregnated tape acquires a desirable level of prestressing.
U.S. Pat. No. 4,456,048 teaches a method of acquiring a change in band stiffness as a function of deflection. The band has a lower stiffness for normal pressurized operation and has a higher stiffness to support load when the tire is uninflated and experiences larger deflection.
Japanese Patent application No. JP 63141809 discloses a run flat tire having a banded element which is formed of layered strips of materials, such as an arramed filament which is impregnated with a high elasticity epoxy resin, which after hardening provides a stiffened band. The tire of this disclosure requires that elastomeric side wall inserts be utilized in combination with the band in order to achieve the desired run flat characteristics.
Other run flat banded pneumatic tires are shown in U.S. Pat. Nos. 4,111,249; 4,318,434; 4,428,411; 4,459,167; and 4,734,144.
Banded tires have been fabricated with band materials made of steel, aluminum, titanium, and epoxy and thermoplastic composites with glass, KEVLAR (aromatic polyamide) and graphite fiber reinforcement. The common failure mode with such lightweight, economical laminate band constructions is interlaminar shear within the band""s primary bending neutral axis. This is a fatigue failure and is directly related to the spectrum of cyclic operating stress. As in all fatigue failures, the lower the stress, the longer the operating life. This problem of fatigue failure occurring along the neutral axis of the band resulting in interlaminar shear can be reduced by the prestressing the band during its manufacture, as described in pending patent application Ser. No. 08/782,364.
Numerous prior art pneumatic tires have been provided with an annular band usually of metal, to resist puncture by sharp objects protruding through the tread area. Although these prior art puncture resistant tires utilizing a metal band provide the desired puncture resistance, in most cases, the metal band effects the ride characteristic of the tire and the life expectancy thereof.
Thus, it is desirable to provide a band element for run flat pneumatic tires and for pneumatic tires having greater puncture resistance, with increased resistance to interlaminar shear stress in the inflated deflected banded tire, the uninflated deflected banded tire and the condition of a banded tire encountering a road surface anomaly, which is accomplished without materially increasing the difficulty of the manufacturing process for producing the band element and without materially increasing the cost thereof. The band element of the present invention achieves these results.
Objectives of the invention include. providing an improved pneumatic tire that is substantially similar in ride, comfort, durability and operation as conventional pneumatic tires, yet which is able to be operated safely at reasonable speeds and for a sufficient number of miles after loss of internal pressurization.
Another objective of the invention is providing such a pneumatic tire and band element therefor which has enhanced load carrying capability, improved endurance by minimizing band stress, and in particular minimizes interlaminar shear stresses heretofore resulting in destruction of the band element.
Still another objective is to provide such a band element for use in a pneumatic tire in which the band element is formed of usual tape strips having longitudinally extending fibers embedded in a resin with the tape being arranged during the construction of the band so that a substantial portion of the fibers extend over the neutral axis of the band which is the area most susceptible to interlaminar shear.
A still further objective of the invention is to provide such a band element for run flat tires in which the individual tape strips which form the band have longitudinally extending fibers embedded within a resin, are twisted into a cylindrical configuration and then pultrated into a rectangular configuration for subsequent wrapping about a mandrel into an annular band having one or more inner and outer layers of the conventional flat tape strips extending about the intermediate pultrated strip layers.
Another objective of the invention is to provide such a band element wherein a plurality of the flat strips containing the longitudinally extending fibers embedded in the resin matrix, are placed in juxtaposition prior to being twisted into a cylindrical configuration for subsequent pultration into a rectangular configuration to provide a stronger layer having the fibers extending across the neutral axis to increase resistance to interlaminar shear.
A still further objective of the invention is to provide such a run flat tire which has increased puncture resistance from the tread contacting road hazards, which can be manufactured at a cost and weight competitive with conventional non run flat tire constructions and which will permit the elimination of a spare tire conventionally required in automobiles thereby providing a cost saving to vehicle manufacturers and owners.
These objectives and advantages are improved by the method of the present invention, the general nature of which may be stated as including a method of forming a thin annular band for embedding in a crown portion of a pneumatic tire including the steps of providing a thin flat strip of material formed with a plurality of longitudinally extending fibers embedded in a resin matrix; twisting the strip until the strip assumes a substantially circular cross section throughout its length; pultrating the twisted strip through a die to provide the strip with a substantially rectangular s cross section; and wrapping the pultrated: strip about a mandrel to form the band having a plurality of adjacent convolutions of said pultrated twisted strip.
These objectives and advantages are further obtained by the improved annular band of the present invention, the general nature of which may be stated as a band for embedding in a crown portion of a pneumatic tire, said band having an axial width and a radial thickness with a neutral axis extending generally through the center of the band in an axial direction, said band further including at least one elongated strip of material having a plurality of longitudinally extending fibers embedded in a resin matrix; said strip being wound into an annular shape having a plurality of adjacent convolutions extending in the axial direction across the band and forming the axial band width, with certain of the longitudinal fibers extending across the neutral axis of the band.
These objectives and advantages are further obtained by providing a pneumatic tire, the general nature of which may be stated as including an elastomeric casing with a tread formed in a crown portion thereof and sidewalls extending from the crown portion to generally circular beads adapted to normally seat themselves in an airtight secured relationship with a wheel; a band member comprising a continuous thin annular composite band fixed in the crown portion of said tire radially inwardly of said tread having an axial width and a radial thickness with a neutral axis extending generally through the center of the band in an axial direction, said band being formed of at least one elongated strip of material having a plurality of longitudinally extending fibers embedded in a resin matrix wound into an annular shape and having a plurality of adjacent convolutions extending in the axial direction across the band and forming the axis width with certain of the longitudinal fibers extending across the neutral axis of the band. dr
Preferred embodiments of the invention, illustrative of the best modes in which applicants have contemplated applying the principles, are set forth in the following description and are shown in the drawings and are particularly and distinctly pointed out and set forth in the appended claims.
FIG. 1 is a sectional view through a pneumatic tire having the improved band element incorporated therein;
FIG. 2 is a diagrammatic side elevational view showing a run flat banded tire in an inflated deflected position;
FIG. 3 is a greatly enlarged fragmentary diagrammatic view showing the forces exerted on a band element in the central footprint region of the inflated deflected banded tire of FIG. 2;
FIG. 4 is a fragmentary diagrammatic view of a multilayered tape composite band prior to deflection;
FIG. 5 is a greatly enlarged diagrammatic view showing the forces exerted on the multilayered tape composite band element of FIG. 4 in the central footprint region of a tire;
FIG. 6 is a fragmentary diagrammatic view with a greatly enlarged end section of a prior art multilayer tape composite band element with each layer being made up of a finite number of widths of tape placed in a side-by-side fashion;
FIG. 7 is a further enlarged view of the encircled portion of FIG. 6;
FIG. 8 is a very diagrammatic view of a conventional tape depicting the fibers extending longitudinally throughout the tape and contained in a resin;
FIG. 9 is a diagrammatic sequence of steps showing the conventional composite tape of FIG. 8 being modified according to the present invention by applying a wrap or twist thereto;
FIG. 10 is a greatly enlarged diagrammatic transverse sectional view of the twisted tape of FIG. 9;
FIG. 11 is a greatly enlarged diagrammatic transverse sectional view of the twisted tape of FIG. 10 being pultruded through a rectangular die;
FIG. 12 is an enlarged diagrammatic side view of a composite multilayered tape band element showing the twisted fibers in the pultruded tape of FIG. 11 extending across the neutral axis;
FIG. 12A is a diagrammatic perspective view showing the twisted pultrated tape strip of FIG. 11 being wound about a mandrel to form at least one layer of a band element;
FIG. 13 is a view similar to FIG. 6 of a first embodiment of a band element of the present invention formed with the pultruded tape of FIG. 11;
FIG. 14 is a further enlarged diagrammatic view of the encircled portion of FIG. 13;
FIG. 15 is a greatly enlarged diagrammatic sectional view of the band element of FIGS. 13 and 14 taken on line 15xe2x80x9415, FIG. 13;
FIG. 16 is a diagrammatic view similar to FIG. 9 showing the sequence of twisting two adjacent tapes;
FIG. 17 is a diagrammatic end view of a band element similar to FIG. 13, formed with the double twisted tape of FIG. 16;
FIG. 18 is a greatly enlarged view of the encircled portion of FIG. 17;
FIG. 19 is a diagrammatic end view similar to FIGS. 13 and 17 of a modified band element in which inside and outside layers are placed in a wrapped relationship with a central layer formed by placing the flat tape of FIG. 8 at approximately 45 degrees relative to the band element axis;
FIG. 20 is a greatly enlarged view of the encircled portion of FIG. 19;
FIG. 21 is a greatly enlarged diagrammatic end view similar to FIGS. 13, 17 and 19 showing a multilayer tape composite band element providing fibers that cross the neutral axis of the band element by having impressions made in the tape layers;
FIG. 22 is a greatly enlarged view of the encircled portion of FIG. 21;
FIG. 23 is a diagrammatic view similar to FIGS. 13, 17, 19 and 21 of a prior art band element formed of homogenous filaments wound in a uniform distribution and embedded in a resin matrix;
FIG. 24 is a greatly enlarged view of the encircled portion of FIG. 23;
FIG. 25 is a view similar to FIGS. 13, 17, 19, 21 and 23 of another embodiment of a band element of the present invention in which the central portion of the band is formed with the pultruded twisted tape as shown in FIG. 11, and with the inner and outer layers being formed of a uniform distribution of wound filament fibers such as shown in FIGS. 23 and 24;
FIG. 26 is a further enlarged diagrammatic view of the encircled portion of FIG. 25;
FIG. 27 is another embodiment of a band element in which the band is formed as a single layer of the pultruded twisted tape as shown in FIG. 11, without any inner and outer layers; and
FIG. 28 is a greatly enlarged view of the encircled portion of FIG. 27.
Similar numerals refer to similar parts throughout the drawings.